This invention relates to a method and apparatus for detecting and preventing fraudulent toll telephone calls using a so-called "blue box".
Those skilled in the art are very familiar with blue boxes so that they need not be described here in detail. Briefly, however, a blue box is a device which a user can couple to a telephone and use to generate signals corresponding to control signals used by toll telephone networks. It can generate a single frequency (SF) tone, e.g. 2600 Hz, as well as multi-frequency (MF) tones. A fraud perpetrator calls a nearby or toll-free destination, thereby seizing a termination toll analogue SF link. He then uses his blue box to apply 2600 Hz tone which fraudulently signals the telephone equipment that the SF link has gone on-hook. Removal of the 2600 Hz signal causes a new seizure at the terminating office which then signals the caller to proceed. The fraud perpetrator then uses his blue box to send new MF digits and reach a new, usually distant, location. However, the telephone system billing equipment records the call as having been to the first caller destination so that the blue box user is not billed properly. For more information on blue boxes, reference may be had to the following:
______________________________________ U.S. Pats. ______________________________________ 4,001,513 Naylor January 4, 1977 4,002,848 Stein January 11, 1977 4,284,851 Schweitzer August 18, 1981 ______________________________________